Radiant gas burner tile



Nov. 9, 1965 c. SAUNDERS ETAL 3,

RADIANT GAS BURNER TILE Filed April 15, 1962 ATTORNEYS.

United States Patent ()fiice 3,216,478 Patented Nov. 9, 1965 3,216,478RADIANT GAS BURNER TILE Alfred C. Saunders, Hamburg, and John F. Grant,Or-

chard Park, N.Y., assignors to Electro Refractories & AbrasivesCorporation, Buffalo, N.Y., acorporation of New York Filed Apr. 13,1962, Ser. No. 187,413 Claims. (Cl. 158-116) This invention relates toceramic bodies through which a mixture of combustible gases is passedand burned close to the face thereof after emergence therefrom. Suchbodies are built into the walls or other portions of ovens or may beplaced on ceilings of covered walk ways for example when it is desiredto transfer heat in the form of radiant energy to bodies or areas atlower temperatures than and at moderate distances from the face of theburner tile. In order that this may be done effectively, it is desirablethat the ignited gases burn as near to the exposed face of the burnertile as possible or even burn within the pores of said tile which areimmediately adjacent the exposed face thereof. In this way the sensibleheat in the burning gases is transferred to the solid tile, raising itstemperature, so that the heat is then transmited in radiant form toareas remote therefrom.

Numerous attempts have been made to utilize this principle but have beenonly partially successful because the exposed face of the burner has notradiated heat sufliciently or because the ignited flame has struck backthrough the tile, igniting the gases on the wrong side thereof, thuscausing explosions or otherwise destroying the unit.

One objective of our invention is to provide a burner tile capable oftransforming a maximum proportion of the sensible heat from the burninggases into radiant energy and transferring this to the desired area.Another objective is to provide a tile through which the flame does notstrike back from the hot face into the chamber in which the combustiblegases are premixed with air or oxygen. A further objective is to providea tile through which a minimum of heat escapes from the furnace unused.Another objective is to provide a tile structure such that the rate offlow of combustible gases therethrough is decreased a minimum amount dueto heating of these gases as the operation proceeds. Still anotherobjective is to provide a burner tile whose face does not develop localareas of high and low temperature but rather glows uniformly all overwith high emission of radiant heat.

In the accompanying drawings FIG. 1 is a sectional elevation of oneexample of a construction of our burner embodying our invention. FIG. 2is a similar section of a burner of modified construction.

In FIG. 1, 1 indicates the ceramic portion of our burner tile as awhole. This comprises a face portion 2 made of relatively coarsegranules of a refractory material having a high emissivity, such forexample as to 30 grit silicon carbide suitably bonded having front andrear faces, and a rear insulating or barrier layer 3 of insulating fireclay grog bonded with a low temperature ceramic binder to hold it inrigid but permeable form which is bonded to the rear face of the faceportion 2. The unit permeability of this portion 3 is somewhat lowerthan that of portion 2 in'order to make sure that flame from the exposedface shall not work its way back through the tile into entering gaschamber 10.

The tile as here illustrated has a further combustion control layer 4 ofquite fine grained insulating material adjacent chamber 10 to furtherinsure against flame Working back through the tile into the chamber.Layer 4 should be relatively thin, perhaps inch, as it is desirable notto restrict gas flow and build up back pressure any more than necessaryfor safety. It is within the scope of our invention to make the granulesof layer 3 so small that the velocity of gas flow through the pores inthat layer is above the velocity of flame propagation so that the flamecannot work back through that layer. In such a case the separatecontrolling layer 4 may be omitted.

Alternatively a fine flame control layer similar to 4' may be built intothe tile as shown in FIG. 2, between layers 2' and 3 or two such controllayers may be provided both between layers 2 and 3 and at the gasentering face of layer 3'. Since except as above described theconstructions shown in FIGS. 1 and 2 are identical, the parts of theceramic block in FIG. 2 which are identical with those of FIG. 1 aredesignated with prime marks so that one description will make bothconstructions readily understood.

Block 1 has a groove 11 out along two or more edges to furnish a seatfor a flanged edge 7 which forms a part of combustion gas box 6 which ismade of suitable metal. In order to assure a tight fit to preventleakage of gas we provide a pad 9 of felted asbestos or refractory woolaround the sides of the tile.

A premixed combustible mixture such as natural gas and air is introducedinto the gas chamber 10 of box 6 through inlet pipe 8 or they may beintroduced separately and mixed in chamber 10. From 10 they flow outwardthrough the pores of the tile to the face of layer 2 where they areignited and allowed to burn. Some combustion works back into the poresof layer 2 as it heats up, thereby raising the temperature of this layerand causing it to radiate heat rapidly. The pores of layer 3 are howeverpreferably so fine that gas velocity through them is high enough toprevent flame from working back into this layer and the pores of layer 4are as explained above very fine so as to completely insure againstflame striking back through this layer.

In order to insure combustion taking place as near as possible to theexposed face of portion 2, we may lightly coat that face with finelydivided catalytic material 5 such as 100 mesh cerium oxide which can beattached by flame spraying or may be dusted on with a temporary binderand fired either along with the tile or later. The effect of thismaterial is to cause maximum flame temperature to develope quickly andin close contact with the tile face.

We prefer in making our burner tile to make it not over 2 /2 inchesthick, divided with A; to /2 inch thickness of coarse grit SiC (forexample 10 to 30 mesh) in layer 2. For layer 3 we use 24 to 30 mesh grogmade of crushed insulating fire brick or mullite making the layerapproximately 1 /2 inches thick and for layer 4 we use As inch of 24 tomesh grog similar to that of layer 3.

As an example of the method of manufacturing our tile, we may proceed asfollows:

First we mix together,

3 90 parts by weight of -30 mesh SiC. 10 parts by weight of 200 meshSiC. 3 parts by weight of dextrin.

and place a layer of this mix inch deep in the mold in which the tile isto be formed.

Next we mix together,

90 parts by weight of 24-30 mesh mullite. 10 parts by weight of Albanyslip clay. 3 parts by weight of dextrin.

and place a layer 1 inches thick of this material on top of the SiClayer already in the mold.

Finally when a third, gas control layer is desired we similarly mixtogether,

88 parts by weight of 24-80 mesh mullite. 12 parts by weight of Albanyslip clay. 3 parts by weight of dextrin.

and place 4; inch of this material in the mold on top of the foregoinglayers. We then press the various layers together under 1000 p.s.i.,remove the pressed piece from the mold and fire it to 2300 F. for 4hours to mature the bond. The tile is thereafter ready for use afterinsertion in box 6.

Obviously the compositions, grit sizes, binders and firing proceduresmay be varied as may be desired as will be understood by those familiarwith the ceramic art. It is important that high strength be maintainedand that materials be so matched that rapid temperature changes shallnot damage the block. We in general find that silicon carbide makes anexcellent hot facing and that backings may be of mullite, fireclay grog,alumina or other compositions with lower thermal conductivity than thesilicon carbide.

Our burner assembly may be suspended from an outer wall by mechanicalsupports attached to the box 6 or may be enclosed in any desired manner,either alone or in groups. Since such supports are not a part of thisinvention they have not been shown.

In operation we like to attain a temperature on the hot face of1800-2000 P. which causes the heated face to radiate heat very rapidly.We find that with the gas and air pressures properly adjusted, thesetemperatures can be maintained with a rear face temperature on the entryface not in excess of 400 F. The flow of gases through such devicestends to decrease as the temperature rises. This is true in our burneralso but with the fine grained control layer shown this change is farless than when it is omitted.

We find that the hot face of our burner arrives at a substantiallyuniform temperature over its entire area, the silicon carbide serving tocarry heat laterally from any particularly hot spot to its surroundingareas.

When the velocity of the combustible gases is main- V tained at such ahigh value as to make it impossible for combustion to be completed whilethey are in contact with the refractory, there is a considerable amountof sensible heat still released in the burning gases after they leavethe burner tile. In such a case, we find it desirable to place a networkof heat resistant wire 12, such as nickel or Inconel screen out in frontof our SiC face. This extracts much of the residual heat from the gasesand transfers it as radiation either directly to the desired area orback to the SiC from whence it is reradiated to the spot to be heated.This network may be secured in any desired manner to the ceramic body,for example, by providing the body with a groove on its edges and theedges of the network may be bent to extend into this groove.

Variations may be made in our burner, either in materials, such as theuse of vother component materials or the mechanical arrangement of thevarious parts within the limits of the following claims.

We claim:

1 A multi-layer burner block for combustible gas burner units whichpermits passage of combustible gases therethrough, comprising:

(a) a facing layer means of bonded silicon carbide granules having afront and a rear face, the size of said granules and the porosity of thelayer means being such that the combustible gases will burn as they arepassed therethrough;

(b) a thermal insulating layer means of bonded ceramic granules which isbonded to the rear face of said facing layer means and through which thecombustible gases are passed to said facing layer means;

(c) said ceramic granules being of smaller size than said siliconcarbide granules and having open pores therebetween;

(d) a thin combustion control layer means of fine bonded ceramicparticles bonded to the back of said thermal insulating layer means; and

(e) the granular size and pores of said combustion control layer meansbeing substantially smaller than said thermal insulating layer means andbeing capable of inhibiting combustion of the combustible gases as theypass therethrough.

2. A multi-layer burner block for combustible gas burner units whichpermits passage of combustible gases therethrough, comprising:

(a) a facing layer means of bonded silicon carbide granules having afront and a rear face, the size of said granules and the porosity of thelayer means being such that the combustible gases will burn as they arepassed therethrough;

(b) a thin combustion control layer means of fine bonded ceramicparticles bonded to the rear face of said facing layer means;

(c) a thermal insulating layer means of bonded ceramic granules which isbonded to the back of said combustion control layer means and throughwhich the combustible gases are passed to said facing layer means;

((1) the ceramic granules of said insulating layer means being ofsmaller size than said silicon carbide granules and having open porestherebetween; and

(e) the granular size and pores of said combustion control layer meansbeing substantially smaller than said thermal insulating layer means andbeing capable of inhibiting combustion of the combustible gases as theypass therethrough.

3. A multi-layer burner block for combustible gas burner units whichpermits passage of combustible gases therethrough, comprising:

(a) a facing layer means of bonded silicon carbide granules having afront and a rear face, the size of said granules and the porosity of thelayer means being such that the combustible gases will burn as they arepassed therethrough;

(b) a barrier layer means of bonded ceramic granules which is bonded tosaid rear face of said facing layer means and through which thecombustible gases are passed to said facing layer means;

(c) said ceramic granules being of smaller size than said siliconcarbide granules;

(d) the pores of said barrier layer means being such that the velocityof combustible gases passing therethrough prevents the flame in saidfacing layer means from traveling back therethrough; and

(e) said barrier layer means being substantially thicker than saidfacing layer means and being of sufficient thickness to provide thermalinsulation between said facing layer means and the combustible gases atthe rear of said barrier layer means.

4. The multi-layer burner block for combustible gas burner units as setforth in claim 3, wherein,

(a) said front face of the facing layer means has a thin coating offinely divided catalytic'material.

5 5. The multi-layer burner block for combustible gas 1,345,377 burnerunits as set forth in claim 3, wherein, 1,901,086 (a) said ceramicgranules are mullite. 2,427,545 3,029,802 References Cited by theExaminer 5 3,073,379

UNITED STATES PATENTS 1,113,171 10/14 Creelrnan 15899 777 1 1,249,36611/17 Fisher 158-99 1,256,301 2/18 Ellis 158-99 1,259,029 3/18 Lucke15899 10 1,308,364 7/19 Lucke 158--99 6 7/ 20 Lirnbarger. 3/33 Cox. 9/47Berger 158-116 4/62 Webster 126-93 1/63 Martin 158-114 FOREIGN PATENTS6/57 Great Britain.

PERCY L. PATRICK, Primary Examiner.

JAMES W. WESTHAVER, Examiner.

3. A MULTI-LAYER BURNER BLOCK FOR COMBUSTIBLE GAS BURNER UNITS WHICHPERMITS PASSAGE OF COMBUSTIBLE GASES THERTHROUGH, COMPRISING: (A) AFACING LAYER MEANS OF BONDED SILICON CARBIDE GRANULES HAVING A FRONT ANDA REAR FACE, THE SIZE OF SAID GRANULES AND THE POROSITY OF THE LAYERMEANS BEING SUCH THAT THE COMBUSTIBLE GASES WILL BURN AS THEY ARE PASSEDTHERETHROUGH; (B) A BARRIER LAYER MEANS OF BONDED CERAMIC GRANULES WHICHIS BONDED TO SAID REAR FACE OF SAID FACING LAYER MEANS AND THROUGH WHICHTHE COMBUSTIBLE GASES ARE PASSED TO SAID FACING LAYER MEANS; (C) SAIDCERAMIC GRANULES BEING OF SMALLER SIZE THAN SAID SILICON CARBIDEGRANULES; (D) THE PORES OF SAID BARRIER LAYER MEANS BEING SUCH THAT THEVELOCITY OF COMBUSTIBLE GASES PASSING THERETHROUGH PREVENTS THE FLAME INSAID FACING LAYER MEANS FROM TRAVELING BACK THERETHROUGH; AND